The present invention relates generally to reed valves for controlling fluid intake into or through fluid passages as in internal combustion engines and the like, and more particularly to improved reed designs that provide significantly improved performance in controlling air and fuel flow in a two-cycle engine while eliminating undesirable back flow and pressure fluctuations into the air/fuel source.
Two cycle engines use an air induction system the efficiency of which is dependent on the precise timing and optimized transfer of air and fuel mixtures drawn into the combustion chamber through an induction path during the suction/pressure stroke of the piston. The method of controlling the intake of a fresh charge into the crankcase of a two-cycle engine has been the subject of much research and investigation. Various devices have been tried in an effort to increase the amount of fresh charge drawn into the crankcase during each operating cycle. Disc valves, piston port valves and reed valves are the most common such devices in use today. Understanding the dynamic behavior of the two-cycle engine reed valves has been found to be relatively difficult due to the unsteady gas flow processes occurring in the exhaust and inlet ducts and the scavenge and combustion processes in the cylinder of a two-cycle type engine.
Reed valves conventionally employ a generally wedge shaped reed cage or block having at least one port covered by a flexible reed. The reed is attached at an upstream end to the reed cage such that its unattached opposite end may be lifted or flexed away from the port by negative pressure or suction created in the engine intake passage, thereby permitting air/fuel to be drawn into the engine. When the differential pressure acting on the reed reaches zero, the reed closes and both air/fuel flow into the engine and back flow through the reed valve is prevented. Reed valves also find application in controlling fluid flow through fluid passages in air conditioning compressors and similar devices to assure flow in only one direction through the associated device.
In high performance two-cycle engines, optimization of reed flex and reflex in reed valves is important to maximizing the piston""s 360 degree cycle so as to charge the combustion chamber with the correct air/fuel mixture at optimum operating engine r.p.m. as it relates to temperature, air density, humidity and elevation. Traditional reed valves used as check valves for preventing back flow of fuel out the intake path of the carburetor employ simple reed petal designs using materials such as steel, fiberglass and epoxy bonded carbon fibers. The known reed designs facilitate relatively inexpensive manufacture, but are considered a compromise in their function to accomplish a complete seal at the induction port. In recent years, the need to accomplish more complete combustion and eliminate unburned fuel from escaping back into the atmosphere has increased due to both popular demand of the public at large and legislative efforts to improve fuel efficiency and reduce unused or spent gases from escaping into the atmosphere. Accordingly, a need exists for reed valves capable of accomplishing these goals while improving the performance of two-cycle engines, particularly at the higher engine r.p.m.
It follows that reed design and selection is critical to achieving maximum horsepower from a two-cycle engine because too much or too little air/fuel entering the engine during each cycle will cause a loss in performance. The amount of air and air/fuel that will flow past the reed is in part dependent on reed size (which is determined by the size of the reed cage ports) and reed flexibility. A flexible reed will allow more airflow than a stiffer reed at lower engine r.p.m., thus increasing low and mid-range acceleration. However, at higher r.p.m. a flexible reed may flutter causing a loss of seal so that a stiffer reed is necessary to control the airflow. Conversely, a stiffer reed will allow less air flow at lower engine r.p.m. and thereby inhibit low range and mid-range operating efficiency.
In addition to reed stiffness, reed response (also referred to as xe2x80x9creflexxe2x80x9d) is also important to improved performance. The faster a reed can respond, i.e., both open and spring back in response to pressure changes acting on the reed, the more accurate the desired volume of fuel and air that will enter the engine crankcase before the reed closes.
It can thus be appreciated that for a given reed cage design, any improvement in the flexibility and response characteristics of the associated reed can add significantly to the performance of the engine with which the reed valve is used throughout the full engine operating range.
A general object of the present invention is to provide a novel reed design for reed valves used to control fluid flow through a fluid passage as in internal combustion engines and other fluid passages.
A more particular object of the present invention is to provide a novel reed design for use in reed valves wherein the reed has significantly improved reflex and port sealing ability.
Another object of the present invention is to provide novel reed designs for use in reed valves wherein each reed has a plurality of petals having selective reflex characteristics such that the various petals are responsive to different pressure forces acting on the petals when disposed in port closing and opening positions on a reed cage or block controlling flow through a fluid passage.
Still another object of the present invention is to provide various novel reed designs for use in reed valves wherein each reed defines a plurality of generally parallel petals each of which is adapted to overlie a port in a reed cage or block, the petals extending in the direction of flow through the reed cage and being integrally interconnected at a hinge end of the reed so that the petals establish axially aligned hinge axes transverse to the petals. The reed petals are selectively configured at their hinge ends to create different reflex characteristics in the petals so that petals corresponding to ports associated with lower pressure zones within the reed cage or block, such as proximate one or more of the reed cage lateral boundary surfaces, are operative to flex open at lower pressures than reed petals that overlie and control flow through ports at higher pressure zones in the reed cage.
In carrying out the present invention, various embodiments of reeds are provided for use with a reed cage or block having a plurality of generally coplanar ports through which fluid may flow from a fluid source, such as a carburetor in an internal combustion engine. Each reed has a plurality of generally parallel reed petals integrally joined at a mounting hinge end of the reed. Each reed petal has generally parallel longitudinal marginal edges that terminate at the hinge end of the petal in predetermined edge surface profiles so as to establish both stress relief and a predetermined hinge width for each petal. The transverse hinge widths of the petals are selectively varied to effect predetermined flex and reflex for the corresponding petals. The hinge widths of the petals associated with one or more lower pressure zones in the reed cage, for example, adjacent one or both of the lateral boundaries of the reed cage depending on the direction of fluid flow into the reed cage, are made smaller than the hinge widths of the petals associated with the higher pressure zones in the reed cage. The outer longitudinal marginal edges of the petals associated with the lower pressure zones in the cage are tapered inwardly at their hinge ends so as to establish a predetermined flex gradient at the hinge end of the petal that differs from the flex at the hinge ends of the petals associated with the higher pressure zones in the reed cage, thereby causing the petals associated with the lower pressure zones to undergo a complex cantilever action and more readily lift from seated sealing positions on their respective reed cage ports and subsequently re-seal the ports. Reed stops are preferably mounted on the reed cage to limit outward flexing of the reed petals from their port closing positions.
The known prior reed designs have reed petals that are of substantially constant lateral width throughout their full lengths, or are otherwise symmetrical about their longitudinal centerlines, and exhibit uniform cantilever flex as they lift about their hinge axis ends. The various reed designs of the present invention undergo a complex cantilever flexing action due to the taper edge profiles provided at the hinge ends of selected petals so that these petals are not symmetrical about their longitudinal centerlines. By selective adjusting of the taper angles, the corresponding petals undergo a progressive change in flex characteristics from their hinge axis throughout the tapered edge profile length of the petal. By selecting a predetermined petal edge profile taper angle and associated hinge axis width, a reed petal may be provided having flex and reflex properties that are optimum for a particular manufacturer""s engine design.
The present invention thus provides reeds for use in reed valves wherein the reed petals undergo a multiple stage lifting relative to each other so that the reeds associated with one or more lower pressure zones in the reed cage or block are operative to flex open or lift from the reed cage at lower pressures (i.e. lower engine r.p.m.) than the one or more reed petals associated with higher pressure zones due to the selective reduction in petal hinge width and the hinge area taper configuration of each outside petal. The wider hinge widths of the one or more petals associated with higher pressure zones in the reed cage create greater rigidity and thereby reduced reflex for the corresponding petals and resist flexing away from their port closing positions at the lower pressures effective to flex open the petals associated with the lower pressure zones, while opening when subjected to increased pressure/suction at higher engine r.p.m., thus effectively producing a multiple-stage reed valve. The reeds are preferably made from carbon-fiber material of selective thickness so that, together with the reed petal hinge configurations, the reed petals resist flutter (defined as the state in which the reed petals do not fully close off their respective cage ports) at maximum engine r.p.m. (i.e. maximum back pressure) when reed oscillation tends to occur in response to reversal of the suction/pressure stroke of the piston.
Further objects and advantages of the present invention will become apparent from the following detailed description of the invention taken in conjunction with the accompanying drawings wherein like reference numerals designate like elements throughout the several views.